A linear light source is well known in which many LEDs are arranged in a line so as to be electrically connected in series and electricity is supplied to each of the LEDs simultaneously. Although the magnitude of the applied voltage necessary for such a series connection is high, since the current to be passed therethrough is the same as that in the case of one LED, a small current is sufficient as a whole and a drive circuit therefor is also simple. Thus there is an advantage in using a series connection in that an efficient device can be realized at low cost. On the other hand, since many LEDs are aligned for use, there is a problem that illumination unevenness occurs in a line illumination due to variations.
A system for avoiding such a problem is known in which a long and thin light guide member (optical guide) corresponding to a linear illumination area is prepared, and light from an LED(s) enters the light guide member from one of end faces or both of the end faces, and then linear illumination of the required area is carried out by the light, which leaks from the light guide member by micro-prisms which are formed and distributed over the light guide member. Since in this type of system, a plurality of LEDs is not arranged in a linear illumination area, even if there are variations in the LEDs, there is an advantage that the illumination unevenness in a linear illumination does not occur. On the other hand, since a few high intensity LEDs are turned on, although the required voltage is low, it is necessary to drive the LEDs with a large current, resulting in a reduction in the efficiency of the electric circuit. Furthermore, there is another problem in that a complicated drive circuit is needed so that the cost thereof becomes high. Moreover, since heat is intensively generated in the LEDs, there is an additional problem in that the temperature of the LEDs themselves becomes high easily.
For example, Japanese Patent Application Publication No. 2006-269140 discloses, as a method for treating heat generation of the LEDs in the aforementioned linear light source with a light guide member and high intensity LEDs, alight guide member made from transparent resin and an LED light source that are fixed to an elongated base. One end face in an axis direction of a rod shape member in a light guide member serves as a light taking-in portion, and the LEDs are arranged to face the light taking-in portion. The LEDs are fixed to an L shaped light source holding portion, and they are fixed to one end of the base, whereby part of heat conducted from the LEDs to the light source holding portion is conducted to the base so that heat is dissipated.
Further, for example, Japanese Patent Application Publication No. 2010-092780 discloses, as a means for efficiently cooling the aforementioned light source holding portion of the base, that a back side of a surface of the light source holding portion of the base, which is bonded to the bottom, is exposed to an air layer, that a convection of heat which passes through a radiating fin portion from the base arises, and that a wind flows into a gap of the fin parts by moving the light source apparatus in a direction perpendicular to an axis of the light guide member.